Nenki Mino is an Iga ninja from the village of Tsubagakure, selected as one of the ten combatants to represent his clan in the war against the Kouga of Manjidani. His most distinguishing feature is his long, tangled black hair, which reaches past his waist but can be extended far beyond its natural length. He possesses complete control over every strand of hair on his body, enabling him to wield it as an extension of his own limbs. He can use his hair to grasp weapons, swing from trees, strangle opponents, or stiffen it into thousands of needle-like projectiles that can pierce and scour his victims. In addition to this ability, he carries a wooden staff, though it is not his primary weapon and serves more for balance or basic strikes.

Nenki is a fierce and capable fighter, but his personality is marked by a rebellious streak. He does not always follow the orders of Tenzen Yakushiji, the de facto commander of the Iga contingent, and frequently questions Tenzen's authority. This independent attitude sets him apart from many of his fellow Iga, though his combat skills make him a valuable asset to the clan. His motivations are driven by loyalty to Iga rather than personal ambition, but his willingness to defy leadership hints at a stubborn, self-reliant nature.

In the story, Nenki plays the role of a mid-tier antagonist for the Kouga. His most notable confrontation is with Okoi Kisaragi, a Kouga ninja whose technique allows her to drain an opponent's blood through skin contact. Because Nenki's entire body is covered in hair, Okoi is unable to make direct contact, and Nenki defeats her by raising his fur and impaling her. Later, he faces Muroga Hyouma, a blind Kouga ninja who possesses the Doujutsu hypnotic eye technique. Unaware that Hyouma is blind and that his Doujutsu is always active, Nenki underestimates his opponent and is killed instantly when Hyouma opens his eyes, turning Nenki's own murderous intent against him.

Key relationships within the Iga include his strained dynamic with Tenzen, whose authority he questions, and his membership among the ten chosen ninja. He shows no particular ties to other Iga members, nor does he display any significant personal development throughout the series. His role is largely defined by his unique hair-based combat style and his early demise at the hands of Hyouma, which serves to demonstrate the lethality of the Kouga's abilities.